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Monitoring the effects of fish farms on wild salmonids

Using an underwater camera sysytem

Project information
  • Categories: rewilding
  • Status: In Progress

Migratory fish such as Atlantic salmon and sea trout play a very important role in their ecosystem but in Ireland, their numbers are a very small fraction of what they once were. One contributor to this sad trend has been the infestation of lice from artificial salmon aquaculture facilities. Sadly, government-led schemes to monitor this issue have been insufficient to tackle the problem so far and much of the impact goes unnoticed. To address this we have partnered with Salmon Watch Ireland on a project to showcase the state of Irish migratory fish populations using an underwater camera. The goal is to increase surveillance where it is lacking and to collect data that can help to address this problem.

Project Timeline

The Intervention

Underwater cameras will be used to live stream videos of these rivers so that the condition of migrating fish can be assessed by anyone online. The Camera system utilises Go Pro Hero 9 technology with underwater WiFi extension cabling allowing the footage to be viewed remotely on an overwater monitor. This technology allows the operator to film at the most opportune periods. Initially, the project will focus on four distinct regions in the southwest of Ireland. Two of them are adjacent to aquaculture farms while the other two are not and will provide a simple means of comparison.

Other than making the videos available online, the levels of infestation with sea lice will also be categorised and reported to Inland Fisheries Ireland and the Marine Institute to allow further inspection and research. This should help prioritise coastal areas for environmental DNA sampling and subsequent quantification of sea lice density.

The project is funded through our business membership with Arctic Stone.

John Murphy from Salmon Watch Ireland holding a camera with an extension pole and blue cables.
John Murphy from Salmon Watch Ireland with the newly acquired camera set up.

Learn More About the Context Behind this Project

Anadromous fish have important ecosystem functions

Atlantic salmon (Salmo salar) and sea trout (Salmo trutta) are anadromous fish. Born in freshwater streams they migrate down to the sea where they feed and grow before migrating back up their natal stream to spawn. By feeding at sea and migrating up Irish rivers they bring nutrients from the marine environment and make them available to inland inhabitants such as Eurasian otters and different birds of prey. Because of this important nutrient transport function, ensuring we have healthy salmonid populations is a way to support the entire ecosystem.

White tailed sea eagle snatching fish from the water.
Other than having intrinsic value, salomonid fish are the food source of many species.

But populations have declined

Unfortunately Atlantic salmon and sea trout populations have been declining in Ireland over the last few decades. One important contributor appears to have been the expansion of artificial salmon aquaculture facilities along the west coast of Ireland. By keeping individuals at high densities these facilities often face problems with sea lice infestations which can spread to adjacent wild fish populations. These parasites feed on the mucus, skin and muscle of the fish and the tissue damage they create leads to physiological stress, a lower feeding rate and a reduced ability to deal with changing water salinity and ultimately can lead to increased mortality. One way sea trout try to cope with this is by migrating to their native rivers prematurely - it is easier for them to cope with freshwater when their skin is damaged and to rid themselves of the lice. This premature return does come with a cost, less time spen feeding at sea means the fish are often small and weak and less capable of making their return journey successfully.

The evidence that sea lice can impact wild salmon populations is also clear. For example, a study published last year shows that salmon in this region are 19 – 46% less likely to return upstream in years with high levels of sea lice in nearby farms.

Close up of sea lice attached to the skin of fish.
Sea lice affect the swimming speed of Atlantic salmon and their ability to survive their arduous migratory journeys.

Underwater video feed

As the project progresses we will keep sharing such videos and start contributing to a more complete picture of the extraordinary journeys of salmonid fish and of the challenges that they are facing due to human activities.

First Grilse recorded on their migration - July 2021

The first Grilse migrating upstream was captured on camera in July 2021. Grilse are young atlantic salmon that are returning to their native rivers for the first time after spending one winter at sea. Note how one individual has been injured by predation.

Salmon and sea trout migrating under difficult conditions - July 2021

On this occasion, John set the camera in a stream with low water levels and elevated temperatures but still detected some juvenile trout and salmon migrating under these difficult circumstances. Salmonids are sensitive to temperature and one of the challenges we face is keeping river temperatures to a level that is suitable to them as the climate warms.

Evidence of sea lice infested sea trout returning prematurely - June 2021

In this video you can see some of the first evidence of heavily infested sea trout captured with the new camera. These fish are about 20 cm and the lesions that are visible on their skin are the result of sea lice tissue damage.

Evidence of sea lice infestation - June 2021

Despite the poor visibility on this one, it is still possible to notice the impact of sea lice. The white patches on the skin indicate the areas where the parasites have caused damage.

Sources & further reading

Peer Reviewed Research Section
  1. β€œLice, infectious disease and taking reef fish: The impact of salmon farms on marine biodiversity” - NoteworthyExternal link
  2. β€œWild Atlantic salmon exposed to sea lice from aquaculture show reduced marine survival and modified response to ocean climate” - ICES Journal of Marine ScienceExternal linkIcon Peer Review
Heart Image

the team behind the project

Team Member

Tiago de Zoeten, conservation biologist at Mossy Earth

Team Member

John Murphy, founder of Salmon Watch Ireland